This invention relates generally to air traffic control systems and more particularly to a method and apparatus for predicting whether maneuvering aircraft will come within distances which are less than established minimum separation standards.
As is known in the art, air traffic control is a service to promote the safe, orderly, and expeditious flow of air traffic. Safety is principally a matter of preventing collisions with other aircraft, obstructions, and the ground; assisting aircraft in avoiding hazardous weather; assuring that aircraft do not operate in airspace where operations are prohibited; and assisting aircraft in distress. Orderly and expeditious flow assures the efficiency of aircraft operations along the routes selected by the operator. It is provided through the equitable allocation of resources to individual flights, generally on a first-come-first-served basis.
As is also known, air traffic control services are provided by air traffic control systems. Air traffic control systems are a type of computer and display system that processes data received from air surveillance radar systems for the detection and tracking of aircraft. Air traffic control systems are used for both civilian and military applications to determine the identity and locations of aircraft in a particular geographic area. Such detection and tracking is necessary to notify aircraft flying in proximity of one another and to warn aircraft that appear to be on a collision course. When the aircraft are spaced by less than a so-called minimum separation standard (MSS) the aircraft are said to xe2x80x9cviolatexe2x80x9d or be in xe2x80x9cconflictxe2x80x9d with the MSS. In this case the air traffic control system provides a so-called xe2x80x9cconflict alert.xe2x80x9d
The merit of a conflict alert (CA) algorithm is measured not only by its ability to predict impending conflicts, but also by how well it avoids making erroneous predictions of conflicts. A conflict between two aircraft approaching each other is said to exist whenever the horizontal distance between the two is less than a horizontal minimum separation standard (HMSS) and, at the same time, the vertical distance between them is less than a vertical minimum separation standard (VMSS). For example, in some situations, aircraft might be required to stay horizontally separated by at least three nautical miles or vertically by at least 1000 feet.
If the velocity of each aircraft is constant, the air traffic control system""s CA function is capable of predicting the potential occurrence of a future conflict, based on the relative position of the aircraft and their velocities. If aircraft are maneuvering, (e.g. accelerating, decelerating including turns), conventional air traffic control systems are only capable of detecting a conflict if an aircraft pair is presently in violation of the vertical separation standards. Thus, if two aircraft approach each other vertically but are not in violation of the vertical minimum separation standard (VMSS), conventional air traffic control systems are unable to predict the conflict and are, therefore, unable to provide a warning of such conflicts before they occur.
To predict conflicts reliably by using tracker-estimated velocities, the latter must be constant and very accurately estimated. These conditions are satisfied for steady state (i.e. straight and at constant velocity) tracks only. When aircraft maneuver, the tracker-estimated velocities are not useful to predict aircraft separation, for a variety of reasons.
One reason is that when targets are approaching each other while maneuvering, they are, in fact, accelerating towards each other. The tracking functions of conventional air traffic control systems, however, do not all estimate acceleration or turn rate. Another reason is that if the CA function were to predict conflict based on the tracker""s current estimated velocity, it would be calculating a slower horizontal approach that might miss the coincidence with the vertical violation and, as a result, not raise an alert. Still another reason why tracker estimated velocities are not accurate is that when a track maneuvers, the accuracy of its velocity estimate is degraded by a maneuver-induced transient. In a turn, the estimated heading usually lags behind the aircraft""s true heading.
One technique for predicting violations of aircraft separation standards in cases where the aircraft""s maneuver dynamics are unknown is referred to as the Maneuver Conflict Prediction (MANCONP) technique. One problem with this technique, however, is that it produces an undesirably large number of false predictions in certain types of aircraft encounters.
It would, therefore, be desirable to provide a technique to predict conflicts between maneuvering aircraft which overcomes the above limitations, which does not require knowledge of the aircraft""s accelerations or headings and which does not provide an excessive number of false alarms.
A technique for reducing the number of false predictions in an air traffic control (ATC) system is provided by utilizing a changeable design parameter and two logical conditions for declaring a violation of minimum separation standard (MSS). The conditions significantly reduce the probability of making a false prediction by shortening the warning time during which a conflict alert (CA) becomes declarable. By properly selecting the magnitude of the design parameter an optimum tradeoff can be established between the lengths of warning times and the rate of false predictions in a given air traffic environment.
The present invention makes use of available information to limit the time interval during which conflict predictions are made to when predictions are most likely to be true. Recognizing that predictions are more likely to be false when the warning time is long, the technique of the present invention establishes a threshold separation distance between two aircraft. The aircraft must reach the threshold separation distance before the system will provide a conflict prediction (i.e. provide an indication of a xe2x80x9chitxe2x80x9d). The maximum separation is provided as a modifiable design parameter value which can be set to fit the air traffic environment in a given airspace (e.g. at a particular airport). Secondly, a restriction is imposed that allows the declaration of a conflict only as long as its estimates indicate a future violation.
The techniques of the present invention can be implemented in aircraft control systems (e.g. such as the Standard Terminal Automation Replacement System or STARS) to add the set of vertically maneuvering aircraft to the class of situations which lend themselves to conflict prediction. By doing so, it enhances the safety function of the air traffic control system. The technique of the present invention can be used to satisfy system requirements such as the requirement that altitude change rate be used to detect conflict between maneuvering aircraft.
The technique of the present invention is portable to a variety of ATC systems including civil and military ATC as well as air defense systems, which normally encounter a much higher percent of maneuvering aircraft than civilian ATC systems.